Investigation, elimination and documentation of VSD faults causing downtime at Mesa A

Abstract

The final aspect of the Engineering degree at Murdoch University is the Internship project. The Internship is a major project done with a company. In this case the Intern did their Internship project with Rio Tinto, at a mine site in the Pilbara called Mesa A. The role of the Intern was to investigate, eliminate and document the faults that were occurring with VSDs for CV102 Stacker Feed Conveyor. These faults were causing unscheduled downtime for the plant which needed to be kept to a minimum.

There were three projects worked on by the Intern. The first project was termed the Out of Sync fault. An Out of Sync fault is when one of the two motors driving the belt of CV102 is running at or above 100% of its capacity while the other motor is idling. At the completion of the Internship the cause of the Out of Sync fault had not been determined. More information is required before a determination of cause/s can be made. There is at present only one date where the fault has occurred and that alarm information is available. Data from the VSD is not available for this event. To make further progress with the project more information needs to be gathered. The event log in the VSD needs to be downloaded at the time of the fault and the alarm data also needs to be downloaded. The gathered information can then be sent to CSE-Uniserve, the company that installed and commissioned the VSDs at Mesa A.

The second project was called the Crash Stop fault. In this fault a cluster of alarms from the VSD prevent the plant being restarted after a crash stop to the plant has occurred. Consulting with CSE-Uniserve and Electricians on site lead to the cause of the fault being identified as due to the communication between the PLC of Motor 1 and Motor 2 with the PLC of the Sync VSD becoming blocked when the power was cut to the VSD and the VSD controllers. The internal UPS was supplying power to the controllers to enable them to send the alarms. The solution 2 was to remove the internal UPS. The wiring changes and the procedures were drawn up. The removal of the UPS was done during the shutdown in October. As well as the removal of the UPS some of the information in Citect, the SCADA package at Mesa A and the PLC were changed so there was no reference to the UPS that had been removed. All that remains as part of this project is to monitor to ensure that there are no unexpected negative impacts as a result of the removal of the UPS. At the time of this report no alarms relating to the VSD after a crash stop have occurred. The plant has only been up a few days since the change so it has not yet been confirmed that the cause of the fault has been eliminated.

The final project of the Internship was to improve the information that was available in Citect to enable better fault finding capabilities in relation to the CV102 VSD faults. To improve the information in Citect more information needed to be gathered. Inside the VSD are Siemens S7-200 PLCs. The plan was to connect to these PLCs and use the information in them to improve Citect, and also to be able to view what is happening in the PLC live, which is useful for fault finding. In order to connect to the PLCs inside the VSDs a new network had to be created. There were complications in the development of this network as there are two separate communications protocols being used by the devices at the present moment. By trying to make another connection to the PLC a third protocol is being introduced. After multiple attempts at designing the new network connections a final design has been drafted. At the completion of the Internship the required equipment had not arrived so the changes had not been made. Another issue with this part of the project is that the program in the PLC is written in Chinese and no-one on site is able to read Chinese. Some University colleagues were able to translate some of the code into English but there was not any back up code for one of the VSDs and the password to access the protected regions of code is not known. This part of the project remains incomplete until the equipment arrives and is installed. Once that is done 3 more information may be able to be included in Citect depending on what is accessible from the PLC.

The Intern finished one project and made significant progress in the other two, getting them to the final design stage, awaiting implementation. Many lessons were learnt by the Intern in terms of technical lessons as well as skills such as project planning, communication and similar skills that are required to be an Engineer.